Sensorimotor System | Sensory and Pain

Stimulus

A physical event that triggers a sensory response

Sensation

Stimulation of sense organs

Perception

Experience (selection, organization, and interpretation) of sensory input

Somatosensation

Senses of touch/pain. Comes from pressure/damage. Cells in skin.

Receptor cell

Specialized cell that responds to a particular energy or substance in the environment that converts into a change in the electric potential.

Labelled lines

The idea that each nerve input reports only a specific type of information (visual distinct from auditory), and there can be different types within a sense (vibration vs pressure vs stretch)

(e.g. auditory pathway! olfaction pathway!)

Receptor potential

Aka generator potential. local change in resting potential of a receptor cell in response to stimuli, could initiate AP

Sensory transduction

The process of a receptor cell converting energy in stimulus into a change in electrical potential across membrane.

Pacinian Corpuscle

A type of mechanoreceptor that responds to vibration and pressure. Located in hypodermis

Meissner’s Corpuscle

A type of mechanoreceptor that responds to changes in light touch.

Merkel’s Discs

A type of mechanoreceptor that detects forms of objects via fine touch/edges. Located in shallow area in dermis.

Ruffini Corpuscles

A type of mechanoreceptor that detects skin stretching. Sparse.

Free Nerve Endings

Detects damages, etc. E.g., pain, itch temperature. Non-specialized mechanoreceptors. Located very shallow.

Receptive fields

Portion of sensory space/stimulus region that can elicit neuronal responses in cell when stimulated. Not equally distributed throughout body (e.g., fingers most sensitive)

Spontaneous (neuronal) activity is normal.

Sensory adaptation

The progressive loss of receptor response as stimulation is maintained. (e.g., wearing a watch)
Phasic receptors display adaptation, while tonic does not.

Dermatome

A strip of skin innervated by a particular spinal nerve.
Cervical (arms, back of head), Thoracic (torso), Lumbar (legs/feet), Sacral (anterior of legs/feet)

Somatosensory Pathway | Dorsal Column System

Tactile sensory cells receive info > Enters dorsal root and ascends > Synapse into neurons in brainstem (medulla), processed contralaterally (decussation) > Thalamus (receives opposite info because of contralateral organization) > Primary Sensory Cortex (S1) > S2 and other cortical areas

Primary Sensory Cortex (S1)

Each hemisphere is located in the postcentral gyrus. Arranged as a map of the body, proportional to density of sensory receptors found in that region. Can influence each other and can change over time.

Polymodal Neurons

Neurons that receive information from several sensory modalities, allowing different sensory systems to interact. (Linked to synesthesia!)

Pain

An unpleasant sensory and emotional experience associated with actual or potential tissue damage.

Sensory-Discriminative dimension

A dimension of pain by the McGill Pain Questionnaire. Throbbing, gnawing, etc.

Motivational-affective dimension

A dimension of pain by the McGill Pain Questionnaire. Emotional dimension; tiring, sickening, fearful. Hard to gauge

Cognitive-evaluative dimension

A dimension of pain by the McGill Pain Questionnaire. None, mild, excruciating. Depends from person to person, can be changed.

Nociceptors

A receptor that responds to stimuli that produce tissue damage or pose the threat of damage

Mediation of pain by nociceptors

Triggered by nociceptors; (1) Damaged nerve cells excite free nerve endings, (2) AP excite blood vessels/mast cells to produce inflammation, (3) mast cells release histamine and chloroquine-like molecule, (4) info enters through dorsal route and synapses on neurons in dorsal horn, (5) glutamate and substance P is released in spinal cord and info is sent across midline into thalamus.

A-delta fiber

Large, myelinated; fast-conducting.

C fiber

Small, unmyelinated; conducts pain information slowly.

Transient receptor potential vanilloid type 1 (TRPVI)

Specialized receptor for temperature. Sensitive to temperature change, capsaicin. Located on C fibers.

Transient receptor potential type M3 (TRPM3)

Sensitive to high temperatures > TRPV1. Located on a-delta fibers, also found in some free nerve ending.

Anterolateral System Pathway | Spinothalamic Tract

Distinct from somatosensory system. Information sent to dorsal horn > Synapse onto spinal neurons (Glutamate and Substance P is released.) > Projection across midline (opposite side) > Thalamus + other cortical areas > Cingulate cortex (part of limbic system)

Neuropathic Pain

Pain that persists long after the injury that started it has healed.

Analgesia

Absence of or reduction in pain.

Gate Control Theory

Perception is controlled by a circuit in the spinal cord which takes into account multiple signals. Additional pathways (touch/top-down processing) can open or close a gate in the spinal cord.

Direct Pathway Model

If nociceptors are stimulated, they will send signal to brain, and person will perceive pain (bottom-up processing). Has issues as pain is affected by mental state, attention, and expectations, also phantom pain!

Types of Pain Management

Pharmacological (Anti-inflammitory drugs, Opiates, Cannabinoids, Spinal blocking), Psychogenic (Hypnosis, CBT), Stimulation (TENS; stimulation of electrical pulses, Acupuncture)